Electronic devices such as a smartphone, a tablet, and the like provide a user with various sounds through a sound output function. Being miniaturized and highly integrated, electronic devices use a micro speaker unit for sound output.
A conventional speaker operates in a manner where sounds (hereinafter respectively referred to as “forward and backward sounds”) are emitted forward and backward with a diaphragm in the center. For example, a speaker mounted on a smartphone transmits the forward sound to a user as an output, and the backward sound is processed at an internal space of an electronic device. However, as smartphones are becoming thinner, these electronic device which includes a conventional micro speaker does not sufficiently secure space through which the backward sound can be emitted, thereby lowering the performance of a sound appliance.